Random access in dynamic and shared spectrums

ABSTRACT

Systems and methods for using a communication system in a spectrum are provided. For example, a random access or RACH procedure may be performed where the random access or RACH procedure may be configured to reduce secondary interference and/or to be used in a pixel-based environment. The random access or RACH procedure may include selecting a RACH preamble; sending a RACH preamble and/or format information; determining a transmission power of the RACH preamble and/or the format information; determining a random access radio network temporary identifier (RA-RNTI) and preamble ID associated with the RACH preamble; and/or selecting a physical RACH (PRACH).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/603,002, filed Feb. 24, 2012; and U.S. ProvisionalPatent Application No. 61/746,797, filed on Dec. 28, 2012; the contentsof which are hereby incorporated by reference herein.

BACKGROUND

Today, communication systems such as communication systems thatimplement LTE (e.g., a LTE system) use various spectrums such as alicensed spectrum, an unlicensed spectrum, a dynamic spectrum, a sharedspectrum, or a combination of these spectrums. For example, an entrantmay not have access to a licensed spectrum and, instead, may deploy aLTE system in a shared spectrum such as TV White Space (TVWS) orIndustrial, Scientific, and Medical (ISM) bands. Such a spectrum may bebroad and may include large numbers of channels often occupied by othertechnologies that make network discovery challenging. Since channels areshared with other operators and other radio access technologies (RATs),such channels are often polluted with localized interferers such ascontrollable and uncontrollable interferers. Additionally, theavailability of such channels often changes over a short period.Accordingly, a LTE system and the bands associated with the LTE systemmay often have to be reconfigured. These reconfigured bands may bereferred to as a dynamic and shared spectrum. Unfortunately, cells suchas small cells deployed in a dynamic and shared spectrum may not be ableto anchor the LTE system to a licensed spectrum. As a result, mobilitymanagement may be a challenge, and the LTE system may need to supportboth uplink and downlink.

To support the uplink, a random access procedure and/or channel, such asa random access channel (RACH), may be used. Unfortunately, wirelesstransmit/receive units (WTRUs), such as user equipment (UE), andinterferences associated therewith, such as secondary WTRUs andinterferences that may be used in a communication system, may provide anumber of problems for a random access procedure. For example, RACHpreamble transmissions may not be recoverable, as a result ofuncontrollable interference (UL transmission). As an example, a WTRU maypoorly estimate path loss due to uncontrollable interference (DLtransmission), resulting in excessive transmit power for a RACH preambleand potential interference to other RACH transmissions from the samecell. As an example, current RACH techniques have gaps to take intoaccount timing uncertainty, and such gaps may be a problem in that theymay allow secondary user transmissions time to access the dynamic andshared spectrum. For LTE standalone solutions using, for example, acoexistence gap mechanism, a RACH capacity may not be enough to supportall IDLE mode WTRUs (e.g., where the dynamic and shared spectrum isnarrow, as is the case in TVWS, where the spectrum allows for a maximumLTE carrier bandwidth of 5 MHz). Also, for LTE standalone solutions, thecoexistence gap mechanism may interfere with the LTE random accessprocedure (e.g., a Release 10 random access procedure) that may havetiming requirements that permit operation of the 6 TDD UL/DLconfigurations including the random access response window (e.g., awindow during which the WTRU expects a response for its random accesspreamble transmission) that may not be received.

SUMMARY

Systems and methods associated with dynamic and spectrum management(DSM) in a communication system, such as a LTE system, may be provided.For example, different systems and methods to support LTE random accesstransmission in a channel shared with other secondary users includingsecondary WTRUs or interfaces may be provided. The systems and methodsmay generally be applied to wireless communication systems that mayimplement LTE (e.g., LTE systems) to, for example, improve a robustnessof a RACH channel used therein.

For example, a random access or RACH procedure may be performed wherethe random access or RACH procedure may be configured to reducesecondary interference and/or may be configured to be used in apixel-based environment. The random access or RACH procedure may includeselecting a RACH preamble. The random access or RACH procedure may alsoinclude sending the RACH preamble and/or format information. The randomaccess or RACH procedure may also include determining a transmissionpower for the RACH preamble and/or the format information. The randomaccess or RACH procedure may also include determining a random accessradio network temporary identifier (RA-RNTI) and preamble ID associatedwith the RACH preamble. The random access or RACH procedure may alsoinclude selecting a physical RACH (PRACH). The random access or RACHprocedure may include any combination of the above steps.

The Summary is provided to introduce in a simplified form a selection ofconcepts that are further described below in the Detailed Description.This Summary is not intended to identify key features or essentialfeatures of the claimed subject matter, nor is it intended to be used tolimit the scope of the claimed subject matter. Furthermore, the claimedsubject matter is not limited to any limitations that solve any or alldisadvantages noted in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A depicts a diagram of an example communications system in whichone or more disclosed examples may be implemented.

FIG. 1B depicts a system diagram of an example wireless transmit/receiveunit (WTRU) that may be used within the communications systemillustrated in FIG. 1A.

FIG. 1C depicts a system diagram of an example radio access network andan example core network that may be used within the communicationssystem illustrated in FIG. 1A.

FIG. 1D depicts a system diagram of an example radio access network andan example core network that may be used within the communicationssystem illustrated in FIG. 1A.

FIG. 1E depicts a system diagram of an example radio access network andan example core network that may be used within the communicationssystem illustrated in FIG. 1A.

FIG. 2 depicts an example of random access formats that may be used in acommunication system, such as a LTE system.

FIG. 3 is a process flow diagram illustrating an example RACH method orprocedure.

FIG. 4 depicts an example of carrier aggregations that may be usedherein.

FIG. 5 depicts an example of cells operating in a dynamic and/or sharedspectrum.

FIG. 6 depicts an example of cells operating in a dynamic and/or sharedspectrum with a licensed macro overlay.

FIG. 7 depicts an example of non-contiguous cells operating in a dynamicand/or shared spectrum with a licensed macro overlay.

FIG. 8 depicts an example of controllable and/or uncontrollablesecondary user interference.

FIG. 9 is a process flow diagram depicting an example method fordetecting a presence of a specific secondary user in an operatingchannel.

FIG. 10 depicts an example of a random access channel (RACH) preambletransmission using Listen Before Talk (LBT).

FIG. 11 depicts an example of a variable length RACH preamble usingsequence repetition.

FIG. 12 depicts an example of one or more rules for random LBT durationand backoff.

FIG. 13 depicts an example of scheduling uplink (UL) transmissions basedon a location.

FIG. 14 depicts an example of UL transmissions that may cause secondaryusers to defer.

FIG. 15 depicts an example of wireless transmit/receive unit (WTRU)transmissions during a C subframe.

FIG. 16 depicts an example of a busy indication that may be carried byWTRUs.

FIG. 17 depicts an example of continuous repeated random accesstransmissions.

FIG. 18 depicts an example of non-continuous repeated random accesstransmissions.

FIG. 19 is a process flow diagram illustrating an example random accessmethod or procedure.

FIG. 20 depicts an example Time-Division Duplex (TDD) frame structureand configuration that may be used cooperatively with a coexistencemechanism.

FIG. 21 depicts an example information exchange between a WTRU and anevolved Node B to coordinate a RACH and a coexistence mechanism.

FIG. 22 depicts an example of a WTRU in idle mode that may be camped onone or more cells.

FIG. 23 depicts an example of preambles such as RACH preambles that maybe used for one or more carriers.

FIG. 24 depicts an example of preambles such as RACH preambles, forexample, staggered in time on one or more carriers.

FIG. 25 depicts an example of preambles such as RACH preambles, forexample, time synchronized on one or more carriers.

FIG. 26 depicts an example of providing pixel location information in acommunication system, such as a LTE system.

FIG. 27 depicts an example of providing power limit information in acommunication system, such as a LTE system.

FIG. 28 depicts an example of providing pixel location information in apreamble such as a RACH preamble that may be used in communicationsystem, such as a LTE system.

FIG. 29 depicts an example of providing location information in a L2/L3message that may be used in a communication system, such as a LTEsystem.

FIG. 30 depicts another example of providing pixel location informationin a communication system, such as a LTE system.

DETAILED DESCRIPTION

A detailed description of illustrative examples will now be describedwith reference to the various Figures. Although this descriptionprovides a detailed example of some possible implementations, it shouldbe noted that the details are intended to be exemplary and in no waylimit the scope of the application.

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed examples may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, and/or 102 d (whichgenerally or collectively may be referred to as WTRU 102), a radioaccess network (RAN) 103/104/105, a core network 106/107/109, a publicswitched telephone network (PSTN) 108, the Internet 110, and/or othernetworks 112, though it will be appreciated that the disclosed examplescontemplate any number of WTRUs, base stations, networks, and/or networkelements. Each of the WTRUs 102 a, 102 b, 102 c, and/or 102 d may be anytype of device configured to operate and/or communicate in a wirelessenvironment. By way of example, the WTRUs 102 a, 102 b, 102 c, and/or102 d may be configured to transmit and/or receive wireless signals andmay include user equipment (UE), a mobile station, a fixed or mobilesubscriber unit, a pager, a cellular telephone, a personal digitalassistant (PDA), a smartphone, a laptop, a netbook, a personal computer,a wireless sensor, consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, and/or 102 d to facilitate access to oneor more communication networks, such as the core network 106/107/109,the Internet 110, and/or the networks 112. By way of example, the basestations 114 a and/or 114 b may be a base transceiver station (BTS), aNode-B, an eNode B, a Home Node B, a Home eNode B, a site controller, anaccess point (AP), a wireless router, and the like. While the basestations 114 a, 114 b are each depicted as a single element, it will beappreciated that the base stations 114 a, 114 b may include any numberof interconnected base stations and/or network elements.

The base station 114 a may be part of the RAN 103/104/105, which mayalso include other base stations and/or network elements (not shown),such as a base station controller (BSC), a radio network controller(RNC), relay nodes, etc. The base station 114 a and/or the base station114 b may be configured to transmit and/or receive wireless signalswithin a particular geographic region, which may be referred to as acell (not shown). The cell may further be divided into cell sectors. Forexample, the cell associated with the base station 114 a may be dividedinto three sectors. Thus, in one example, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother example, the base station 114 a may employ multiple-inputmultiple output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a and/or 114 b may communicate with one or more ofthe WTRUs 102 a, 102 b, 102 c, and/or 102 d over an air interface115/116/117, which may be any suitable wireless communication link(e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV),visible light, etc.). The air interface 115/116/117 may be establishedusing any suitable radio access technology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 103/104/105 and the WTRUs 102a, 102 b, and/or 102 c may implement a radio technology such asUniversal Mobile Telecommunications System (UMTS) Terrestrial RadioAccess (UTRA), which may establish the air interface 115/116/117 usingwideband CDMA (WCDMA). WCDMA may include communication protocols such asHigh-Speed Packet Access (HSPA) and/or Evolved HSPA (HSPA+). HSPA mayinclude High-Speed Downlink Packet Access (HSDPA) and/or High-SpeedUplink Packet Access (HSUPA).

The base station 114 a and the WTRUs 102 a, 102 b, and/or 102 c mayimplement a radio technology such as Evolved UMTS Terrestrial RadioAccess (E-UTRA), which may establish the air interface 115/116/117 usingLong Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

The base station 114 a and the WTRUs 102 a, 102 b, and/or 102 c mayimplement radio technologies such as IEEE 802.16 (i.e., WorldwideInteroperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1X,CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95(IS-95), Interim Standard 856 (IS-856), Global System for Mobilecommunications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSMEDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. The basestation 114 b and the WTRUs 102 c, 102 d may implement a radiotechnology such as IEEE 802.11 to establish a wireless local areanetwork (WLAN). The base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.15 to establish a wirelesspersonal area network (WPAN). The base station 114 b and the WTRUs 102c, 102 d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM,LTE, LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG.1A, the base station 114 b may have a direct connection to the Internet110. Thus, the base station 114 b may not be required to access theInternet 110 via the core network 106/107/109.

The RAN 103/104/105 may be in communication with the core network106/107/109, which may be any type of network configured to providevoice, data, applications, and/or voice over internet protocol (VoIP)services to one or more of the WTRUs 102 a, 102 b, 102 c, and/or 102 d.For example, the core network 106/107/109 may provide call control,billing services, mobile location-based services, pre-paid calling,Internet connectivity, video distribution, etc., and/or performhigh-level security functions, such as user authentication. Although notshown in FIG. 1A, it will be appreciated that the RAN 103/104/105 and/orthe core network 106/107/109 may be in direct or indirect communicationwith other RANs that employ the same RAT as the RAN 103/104/105 or adifferent RAT. For example, in addition to being connected to the RAN103/104/105, which may be utilizing an E-UTRA radio technology, the corenetwork 106/107/109 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106/107/109 may also serve as a gateway for the WTRUs102 a, 102 b, 102 c, and/or 102 d to access the PSTN 108, the Internet110, and/or other networks 112. The PSTN 108 may includecircuit-switched telephone networks that provide plain old telephoneservice (POTS). The Internet 110 may include a global system ofinterconnected computer networks and devices that use commoncommunication protocols, such as the transmission control protocol(TCP), user datagram protocol (UDP) and the Internet protocol (IP) inthe TCP/IP Internet protocol suite. The networks 112 may include wiredor wireless communications networks owned and/or operated by otherservice providers. For example, the networks 112 may include anothercore network connected to one or more RANs, which may employ the sameRAT as the RAN 103/104/105 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, and/or 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, and/or 102 d may include multipletransceivers for communicating with different wireless networks overdifferent wireless links. For example, the WTRU 102 c shown in FIG. 1Amay be configured to communicate with the base station 114 a, which mayemploy a cellular-based radio technology, and with the base station 114b, which may employ an IEEE 802 radio technology.

FIG. 1B depicts a system diagram of an example WTRU 102. As shown inFIG. 1B, the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements. Also, the basestations 114 a and 114 b, and/or the nodes that base stations 114 a and114 b may represent, such as but not limited to transceiver station(BTS), a Node-B, a site controller, an access point (AP), a home node-B,an evolved home node-B (eNodeB), a home evolved node-B (HeNB), a homeevolved node-B gateway, and proxy nodes, among others, may include someor all of the elements depicted in FIG. 1B and described herein.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 115/116/117. For example, the transmit/receiveelement 122 may be an antenna configured to transmit and/or receive RFsignals. The transmit/receive element 122 may be an emitter/detectorconfigured to transmit and/or receive IR, UV, or visible light signals,for example. The transmit/receive element 122 may be configured totransmit and receive both RF and light signals. It will be appreciatedthat the transmit/receive element 122 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, the WTRU 102 may include two or moretransmit/receive elements 122 (e.g., multiple antennas) for transmittingand receiving wireless signals over the air interface 115/116/117.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. The processor 118 may access information from, and storedata in, memory that is not physically located on the WTRU 102, such ason a server or a home computer (not shown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 115/116/117from a base station (e.g., base stations 114 a, 114 b) and/or determineits location based on the timing of the signals being received from twoor more nearby base stations. It will be appreciated that the WTRU 102may acquire location information by way of any suitablelocation-determination method.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C depicts a system diagram of the RAN 103 and the core network 106according to an example. As noted above, the RAN 103 may employ a UTRAradio technology to communicate with the WTRUs 102 a, 102 b, and/or 102c over the air interface 115. The RAN 103 may also be in communicationwith the core network 106. As shown in FIG. 1C, the RAN 103 may includeNode-Bs 140 a, 140 b, and/or 140 c, which may each include one or moretransceivers for communicating with the WTRUs 102 a, 102 b, and/or 102 cover the air interface 115. The Node-Bs 140 a, 140 b, and/or 140 c mayeach be associated with a particular cell (not shown) within the RAN103. The RAN 103 may also include RNCs 142 a and/or 142 b. It will beappreciated that the RAN 103 may include any number of Node-Bs and RNCs.

As shown in FIG. 1C, the Node-Bs 140 a and/or 140 b may be incommunication with the RNC 142 a. Additionally, the Node-B 140 c may bein communication with the RNC 142 b. The Node-Bs 140 a, 140 b, and/or140 c may communicate with the respective RNCs 142 a, 142 b via an Iubinterface. The RNCs 142 a, 142 b may be in communication with oneanother via an Iur interface. Each of the RNCs 142 a, 142 b may beconfigured to control the respective Node-Bs 140 a, 140 b, and/or 140 cto which it is connected. In addition, each of the RNCs 142 a, 142 b maybe configured to carry out or support other functionality, such as outerloop power control, load control, admission control, packet scheduling,handover control, macrodiversity, security functions, data encryption,and the like.

The core network 106 shown in FIG. 1C may include a media gateway (MGW)144, a mobile switching center (MSC) 146, a serving GPRS support node(SGSN) 148, and/or a gateway GPRS support node (GGSN) 150. While each ofthe foregoing elements are depicted as part of the core network 106, itwill be appreciated that any one of these elements may be owned and/oroperated by an entity other than the core network operator.

The RNC 142 a in the RAN 103 may be connected to the MSC 146 in the corenetwork 106 via an IuCS interface. The MSC 146 may be connected to theMGW 144. The MSC 146 and the MGW 144 may provide the WTRUs 102 a, 102 b,and/or 102 c with access to circuit-switched networks, such as the PSTN108, to facilitate communications between the WTRUs 102 a, 102 b, and/or102 c and traditional landline communications devices.

The RNC 142 a in the RAN 103 may also be connected to the SGSN 148 inthe core network 106 via an IuPS interface. The SGSN 148 may beconnected to the GGSN 150. The SGSN 148 and the GGSN 150 may provide theWTRUs 102 a, 102 b, and/or 102 c with access to packet-switchednetworks, such as the Internet 110, to facilitate communications betweenand the WTRUs 102 a, 102 b, and/or 102 c and IP-enabled devices.

As noted above, the core network 106 may also be connected to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

FIG. 1D depicts a system diagram of the RAN 104 and the core network 107according to an example. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b,and/or 102 c over the air interface 116. The RAN 104 may also be incommunication with the core network 107.

The RAN 104 may include eNode-Bs 160 a, 160 b, and/or 160 c, though itwill be appreciated that the RAN 104 may include any number of eNode-Bs.The eNode-Bs 160 a, 160 b, and/or 160 c may each include one or moretransceivers for communicating with the WTRUs 102 a, 102 b, and/or 102 cover the air interface 116. The eNode-Bs 160 a, 160 b, and/or 160 c mayimplement MIMO technology. Thus, the eNode-B 160 a, for example, may usemultiple antennas to transmit wireless signals to, and receive wirelesssignals from, the WTRU 102 a.

Each of the eNode-Bs 160 a, 160 b, and/or 160 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 1D, theeNode-Bs 160 a, 160 b, and/or 160 c may communicate with one anotherover an X2 interface.

The core network 107 shown in FIG. 1D may include a mobility managementgateway (MME) 162, a serving gateway 164, and a packet data network(PDN) gateway 166. While each of the foregoing elements are depicted aspart of the core network 107, it will be appreciated that any one ofthese elements may be owned and/or operated by an entity other than thecore network operator.

The MME 162 may be connected to each of the eNode-Bs 160 a, 160 b,and/or 160 c in the RAN 104 via an S1 interface and may serve as acontrol node. For example, the MME 162 may be responsible forauthenticating users of the WTRUs 102 a, 102 b, and/or 102 c, beareractivation/deactivation, selecting a particular serving gateway duringan initial attach of the WTRUs 102 a, 102 b, and/or 102 c, and the like.The MME 162 may also provide a control plane function for switchingbetween the RAN 104 and other RANs (not shown) that employ other radiotechnologies, such as GSM or WCDMA.

The serving gateway 164 may be connected to each of the eNode-Bs 160 a,160 b, and/or 160 c in the RAN 104 via the S1 interface. The servinggateway 164 may generally route and forward user data packets to/fromthe WTRUs 102 a, 102 b, and/or 102 c. The serving gateway 164 may alsoperform other functions, such as anchoring user planes duringinter-eNode B handovers, triggering paging when downlink data isavailable for the WTRUs 102 a, 102 b, and/or 102 c, managing and storingcontexts of the WTRUs 102 a, 102 b, and/or 102 c, and the like.

The serving gateway 164 may also be connected to the PDN gateway 166,which may provide the WTRUs 102 a, 102 b, and/or 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, and/or 102 c andIP-enabled devices.

The core network 107 may facilitate communications with other networks.For example, the core network 107 may provide the WTRUs 102 a, 102 b,and/or 102 c with access to circuit-switched networks, such as the PSTN108, to facilitate communications between the WTRUs 102 a, 102 b, and/or102 c and traditional landline communications devices. For example, thecore network 107 may include, or may communicate with, an IP gateway(e.g., an IP multimedia subsystem (IMS) server) that serves as aninterface between the core network 107 and the PSTN 108. In addition,the core network 107 may provide the WTRUs 102 a, 102 b, and/or 102 cwith access to the networks 112, which may include other wired orwireless networks that are owned and/or operated by other serviceproviders.

FIG. 1E depicts a system diagram of the RAN 105 and the core network 109according to an example. The RAN 105 may be an access service network(ASN) that employs IEEE 802.16 radio technology to communicate with theWTRUs 102 a, 102 b, and/or 102 c over the air interface 117. As will befurther discussed below, the communication links between the differentfunctional entities of the WTRUs 102 a, 102 b, and/or 102 c, the RAN105, and the core network 109 may be defined as reference points.

As shown in FIG. 1E, the RAN 105 may include base stations 180 a, 180 b,and/or 180 c, and an ASN gateway 182, though it will be appreciated thatthe RAN 105 may include any number of base stations and ASN gateways.The base stations 180 a, 180 b, and/or 180 c may each be associated witha particular cell (not shown) in the RAN 105 and may each include one ormore transceivers for communicating with the WTRUs 102 a, 102 b, and/or102 c over the air interface 117. The base stations 180 a, 180 b, and/or180 c may implement MIMO technology. Thus, the base station 180 a, forexample, may use multiple antennas to transmit wireless signals to, andreceive wireless signals from, the WTRU 102 a. The base stations 180 a,180 b, and/or 180 c may also provide mobility management functions, suchas handoff triggering, tunnel establishment, radio resource management,traffic classification, quality of service (QoS) policy enforcement, andthe like. The ASN gateway 182 may serve as a traffic aggregation pointand may be responsible for paging, caching of subscriber profiles,routing to the core network 109, and the like.

The air interface 117 between the WTRUs 102 a, 102 b, and/or 102 c andthe RAN 105 may be defined as an R1 reference point that implements theIEEE 802.16 specification. In addition, each of the WTRUs 102 a, 102 b,and/or 102 c may establish a logical interface (not shown) with the corenetwork 109. The logical interface between the WTRUs 102 a, 102 b,and/or 102 c and the core network 109 may be defined as an R2 referencepoint, which may be used for authentication, authorization, IP hostconfiguration management, and/or mobility management.

The communication link between each of the base stations 180 a, 180 b,and/or 180 c may be defined as an R8 reference point that includesprotocols for facilitating WTRU handovers and the transfer of databetween base stations. The communication link between the base stations180 a, 180 b, and/or 180 c and the ASN gateway 182 may be defined as anR6 reference point. The R6 reference point may include protocols forfacilitating mobility management based on mobility events associatedwith each of the WTRUs 102 a, 102 b, and/or 102 c.

As shown in FIG. 1E, the RAN 105 may be connected to the core network109. The communication link between the RAN 105 and the core network 109may defined as an R3 reference point that includes protocols forfacilitating data transfer and mobility management capabilities, forexample. The core network 109 may include a mobile IP home agent(MIP-HA) 184, an authentication, authorization, accounting (AAA) server186, and a gateway 188. While each of the foregoing elements aredepicted as part of the core network 109, it will be appreciated thatany one of these elements may be owned and/or operated by an entityother than the core network operator.

The MIP-HA may be responsible for IP address management, and may enablethe WTRUs 102 a, 102 b, and/or 102 c to roam between different ASNsand/or different core networks. The MIP-HA 184 may provide the WTRUs 102a, 102 b, and/or 102 c with access to packet-switched networks, such asthe Internet 110, to facilitate communications between the WTRUs 102 a,102 b, and/or 102 c and IP-enabled devices. The AAA server 186 may beresponsible for user authentication and for supporting user services.The gateway 188 may facilitate interworking with other networks. Forexample, the gateway 188 may provide the WTRUs 102 a, 102 b, and/or 102c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, and/or 102 cand traditional landline communications devices. In addition, thegateway 188 may provide the WTRUs 102 a, 102 b, and/or 102 c with accessto the networks 112, which may include other wired or wireless networksthat are owned and/or operated by other service providers.

Although not shown in FIG. 1E, it should, may, and/or will beappreciated that the RAN 105 may be connected to other ASNs and the corenetwork 109 may be connected to other core networks. The communicationlink between the RAN 105 the other ASNs may be defined as an R4reference point, which may include protocols for coordinating themobility of the WTRUs 102 a, 102 b, and/or 102 c between the RAN 105 andthe other ASNs. The communication link between the core network 109 andthe other core networks may be defined as an R5 reference, which mayinclude protocols for facilitating interworking between home corenetworks and visited core networks.

Systems and methods for supporting random access transmissions includingrandom access channels (RACHs) may be provided. In an example, aprocedure may be provided in which the WTRU may listen to a channelduring a RACH subframe, for example, before sending an LTE RACHpreamble, and may send the RACH preamble if the channel may be free ormay become free during the RACH subframe. The WTRU may also send theRACH preamble if such a transmission fits in the time remaining in aRACH opportunity that may include single or multiple subframes. Thesensing may also use feature detection.

A procedure may be provided in which a WTRU may send consecutive andsmall RACH preambles within a single RACH subframe. The number ofpreambles may depend on time remaining after the medium may be sensedfree.

A procedure may also be provided in which a WTRU may send a single smallRACH preamble in the RACH subframe. The time of transmission of such apreamble may be randomly selected to minimize the possibility ofcollision between different WTRUs.

A procedure may also be provided in which a WTRU may take a RACHtransmission time within the RACH subframe into account prior toadjusting the timing advance sent by the base station. The timingadvance may be sent assuming a RACH transmission at the start of asubframe.

A procedure may further be provided in which a base station may rely onconnected mode WTRUs to force secondary users to defer transmissionsassociated therewith, for example, by sending a known transmission inthe UpPTS portion of the special subframe, by sending a known packet ina randomly selected resource block in a special reserved subframe,and/or by sending a busy indication on some sub-carriers or resourceblocks according to a fixed and known pattern.

A procedure may be provided in which a preamble may be repeated over anextended random access transmit window (e.g., over multiple subframes)and where the RA-RNTI may be based on the last subframe in the window.

A procedure may also be provided in which a base station may be capableof detecting a preamble collision based on pattern of preambles receivedin an extended random access transmit window or timing adjustment valuessuch that collisions may be resolved.

A procedure may be provided in which carrier aggregation (CA) capableWTRUs may camp on multiple cells and may send or receive RACH preambleover multiple cells possibly staggered in time and possibly using sameor different preambles.

A procedure may also be provided in which an eNB that may receive one ormore RACH preamble transmissions on multiple cells may select a cell(e.g., the best cell) for sending the downlink preamble responsemessage.

Furthermore, a procedure may include providing (e.g., transmittingand/or sending) a WTRU with pixel information and pixel-based transmitpower information through, for example, system information. According toan example, a set of procedures may further be provided for a WTRU tosend location information to an eNB (e.g., through RACH preambles or aspart of a RACH L2/L3 message) such that the eNB may use such locationinformation to provide the WTRU with pixel-based transmit powerinformation.

A random access or RACH method (e.g., procedure or operation) that maybe used in a communication system, such as an LTE system may be used asan uplink mechanism for one or more of a number of reasons. A randomaccess or RACH method may be used for initial access when establishingan RRC connection and/or for re-establishing a radio link after a radiolink failure. A random access or RACH method may also be used forhandover when uplink synchronization may be used for a new target cell.A random access or RACH method may also be used for establishing uplinksynchronization if UL or DL data may arrive when a terminal may be RRCconnected and uplink may not be synchronized. A random access or RACHmethod may also be used for positioning. Further, a random access orRACH method may be used for transmitting a scheduling request if nodedicated scheduling request resource may be configured. A random accessor RACH method may be used for any combination of the above or otherreasons.

A RACH method that may be used in a communication system, such as a LTEsystem, may be designed, keeping in mind low latency, good detectionprobability at low SNR, minimum overhead, and minimum interferencegenerated to adjacent scheduled Physical Uplink Shared Channel/PhysicalUplink Control Channel (PUSCH/PUCCH) transmission. A WTRU that may beused in such a communication system may transmit a random access (RA)preamble during a RACH attempt. The RA preamble may include a Zadoff-Chusequence that may have suitable auto and cross correlation properties.An eNB that may be used in such a communication system may also have theflexibility to use one of a number, e.g., 5 RA preamble formats. FIG. 2,for example, depicts four Preamble Formats 200, 202, 204, and 206. Eachpreamble may be preceded with a cyclic prefix (CP). Different formatsmay be used depending on a size of the cell. Preamble format 200, forexample, may be used with a 1 ms window. Preamble formats 202 and 204may be used with a 2 ms window. Preamble format 206 may be used with a 3ms window.

Each cell may have a number of random access opportunities, for example,each of which may occupy, e.g., six consecutive resource blocks. ForFDD, there may be one random access opportunity per subframe, but theconfiguration may have multiple random access opportunities per frame.To deal with a potential asymmetric UL/DL frame structure, aTime-Division Duplex (TDD) multiple random access opportunities mayexist per subframe (e.g., up to 6). Details about a random accessopportunity may be broadcast in system information through anInformation Element (IE), such as a prach-ConfigurationIndex, forexample.

FIG. 3 illustrates a RACH method or procedure 300 that may be used orimplemented in a communication system. At 302, a WTRU may transmit apreamble. Details for such a preamble transmission may be broadcast in acell's system information, e.g., “preamble set,” “transmission resourcesand opportunity,” and/or “RA format.” The WTRU may randomly select“preamble” and “opportunity” and may generate a particular preambleformat. The WTRU may also determine the transmit power for such apreamble based on a path loss calculation from a DL reference signaland/or broadcast parameters, such as desired received power (SINR),power ramping step, preamble-based offset, and the like.

The eNB may detect several simultaneous preamble transmissions in thesame time frequency PRACH resources. Based on a selected opportunity,the WTRU may be assigned an RA-RNTI. The RA-RNTI may be associated withthe PRACH in which the Random Access Preamble may be transmitted,RA-RNTI=1+t_id+10*f_id, where t_id may be the index of the firstsubframe of the specified PRACH (0≦t_id<10), and f_id may be the indexof the specified PRACH within that subframe, in ascending order offrequency domain (0≦f_id<6).

At 304, an eNB may correlate a received signal in each PRACH opportunitywith the possible preamble sequences. As a result of such a correlation,the eNB may correctly detect multiple preambles. It may be possible thattwo WTRUs used the same preamble in the same transmission opportunity(e.g., resulting in a collision). Such a collision may resolved at 308(e.g., contention resolution). Upon detection of a preamble in atransmission opportunity, the eNB may determine a RA-RNTI. The eNB maythen signal one or more of the following to the WTRU (addressed to theRA-RNTI): timing adjustment information; uplink grant to the UE;preamble identifier; and/or temporary C-RNTI.

For example, the WTRU may monitor a PDCCH for Random Access Response(s)identified by the RA-RNTI within the RA Response window. The RA ResponseWindow may start at a subframe that includes the end of the preambletransmission plus three subframes and may have a length of“ra-ResponseWindowSize” subframes (see Table 1 below). If the RAResponse may not be received within the configured time window, the WTRUmay retransmit the preamble after a suitable backoff, and with aconfigured ramp up in transmit power. If the RA Response may be found inthe configured time window, the WTRU may check for a match in thePreamble Identifier. A match may imply a successful random accessresponse. In such a case, the WTRU may apply the Timing Advance and mayprocess the UL grant to send the L3 message (e.g., RRC ConnectionRequest, TA Update). At such a point, a collision may occur in the RACHtransmission. If there may be no match, the WTRU may declare a randomaccess failure and may retransmit the preamble after a suitable backoff,and with a configured ramp up in transmit power.

TABLE 1 Random Access Response Window Configurationra-ResponseWindowSize ENUMERATED {sf2, sf3, sf4, sf5, sf6, sf7, sf8,sf10}

At 306 (e.g., of the RACH method 300), the WTRU may use the UL grant tosend the uplink transmission on PUSCH (e.g., HARQ may be used for such atransmission). The WTRU may also send the temporary C-RNTI allocated byeNB and the C-RNTI/S-TMSI if the WTRU may already have one or 48-bitWTRU identity (IMSI). A 48-bit WTRU identity may facilitate contentionresolution. In case of a collision, several WTRUs may each interpretthat the grant may be for them and may respond with a L3 message.

According to an example, the base station may choose one of the mobileidentities. If there may be no collision at 304, one mobile identity maybe available to the UE. The eNB may respond with the identity of theselected WTRU in a contention resolution message. The WTRU mayacknowledge such a reception (e.g., through HARQ feedback) that maycomplete the random access procedure (e.g., RACH method). In case of acollision, the WTRU that may not receive the contention resolutionmessage may consider such a transmission a failure and may reattempt adifferent (or new) RACH transmission.

Two or more (e.g., up to 5) component carriers (CCs) in LTE, such asLTE-Advanced, may be aggregated to support wider transmission bandwidthsup to 100 MHz. For example, a UE, depending on the capabilitiesassociated therewith, may simultaneously receive or transmit on one ormore CCs. The WTRU may also be capable of aggregating a different numberof differently sized CCs in an uplink (UL) or a downlink (DL). Carrieraggregation (CA) may be supported for both contiguous and non-contiguousCCs. Three examples may be used as shown in FIG. 4. For example, asshown at 402, intra-band contiguous CA may be used where multipleadjacent CCs may be aggregated to produce contiguous bandwidth widerthan 20 MHz. As shown at 404, intra-band non-contiguous CA wheremultiple CCs that may belong to the same bands (but may not be adjacentto one another) may be aggregated and used in a non-contiguous manner.As shown at reference numeral 406, inter-band non-contiguous CA may beused where multiple CCs that may belong to different bands may beaggregated. These CA techniques may be used individually or incombination with one another.

CA, such as CA LTE-A included in Release 10 3GPP, may increase a datarate achieved by a communication system such as a LTE system by allowinga scalable expansion of the bandwidth delivered to a user by allowingsimultaneous utilization of the radio resources in multiple carriers. CAmay also enable or allow backward compatibility of the system and legacyWTRUs (e.g., Release 8 and 9 compliant WTRUs) such that the WTRUs mayfunction within a system such as an LTE system with CA deployed (e.g.,where Release 10 with CA is deployed).

A number of potential options, methods, or techniques may be availablefor the potential use of the dynamic and shared spectrum (e.g., TVWS,ISM or other LE) bands. For example, some operators may rely on usingthe unlicensed band for CA such that resulting component carriers may beused to create supplementary cells (SuppCells) that may be aggregatedwith the primary cell (PCell). A communication system, such as an LTEsystem, may dynamically change a SuppCell from one unlicensed frequencychannel to another. The use of such a change, which may not be presentin an example of a communication system, such as an LTE-A systemcompliant with, for example, Release 10, may be due to a presence ofinterference and potentially primary users in unlicensed bands. Forexample, a strong interference such as a microwave oven or a cordlessphone may make a particular channel in an ISM band unusable for datatransmission. In addition, when dealing with TVWS channels as unlicensedchannels, a user of such channels may evacuate a channel upon thearrival of a system that may have exclusive rights to use that channel(e.g., TV broadcast or wireless microphone in the case of the TVWS).Furthermore, the nature of unlicensed bands and an increase in thenumber of wireless systems that may make use of such bands mayinherently result in relative quality of channels within a licensed bandchanging dynamically. To adjust to this, a communication system such asan LTE system performing CA may be able to dynamically change from aSuppCell in an unlicensed channel to another in order or to reconfigureitself in order to operate on a different frequency.

Additionally, some operators may deploy (e.g., may want to deploy)cellular technology in areas where there may be little or no macro cellcoverage. The cost and return on investment of extending macro coverageto these areas may not make such an approach viable. Instead, suchoperators may decide to deploy a standalone TVWS solution (e.g., nolicensed carrier) using small cells to manage a coverage hole.

Some operators may also deploy (e.g., may want to deploy) a standalonesolution as an alternative to roaming. For example, a particularlocation operator (e.g., a North American operator) may rely on astandalone deployment scenario in a different location operator (e.g., aEuropean operator) such that the different location operator (e.g., theEuropean operator) may be bypassed and may potentially offer savings toend customers.

Some operators or traditional operators may also benefit (or may want tobenefit) from deploying LTE in dynamic and shared spectrum for a numberof reasons including: mitigating and avoiding small cell to macro cellinterference, for example, by using dynamic and shared spectrum insteadof a licensed spectrum in the small cell layer; using tiered service(s)including small cells that may be deployed to service low mobilityapplications such as M2M; and/or capacity enhancements.

Some new operators (e.g., new entrants) may use unlicensed bands todeploy their own networks. Such new entrants may not rely on thetraditional/licensed cellular operators, but they may need to adaptcellular technologies so they may deploy their networks using smallcells in shared and dynamic spectrum such as TVWS. Such deploymentstypically may be standalone, without relying on any licensed carriers.There may be a number of motivations for such new entrants to deploytheir own network. For example, traditional/licensed cellular operatorsmay often act as gatekeepers, and they may tend to block new servicessuch that the deployment of such a standalone network deployment, evenin a non-ubiquitous fashion, would allow the new entrants to showcase orintroduce these new services to end customers. Further, such new entrantplayers may not have a monthly billing relationship with end customers,and the basic connectivity provided by the small cell network may enablethese new entrants to develop new business models (e.g., based onadvertising). Also, such new entrant players often make devices that maynot have cellular connectivity to address market segment for users thatmay not to pay a high monthly fee (e.g., tablets or e-readers). Inaddition, some new entrant players may have already made considerableinvestment in developing and lobbying TVWS technology.

As a result of a transition from analog to digital TV transmissions inthe 470-862 MHz frequency band, portions of a spectrum may no longer beused for TV transmissions, although the amount and exact frequency ofunused spectrum may vary from location to location. Such unused portionsof spectrum are referred to as TV White Space (TVWS). The FCC has openedup such TVWS frequencies for a variety of unlicensed uses. The use ofTVWS disclosed herein may include the opportunistic use of White Spacein the 470-790 MHz bands. Such frequencies may be exploited by secondaryusers for any radio communication given that the secondary users may notbe interfering with other incumbent/primary users. As a result, the useof LTE and other cellular technologies within the TVWS bands may bepossible and may have been considered (e.g., in ETSI RRS). Use of LTE inother unlicensed bands, such as the ISM band, may also possible.

Various options are available for using a dynamic and shared spectrum ina communication system such as a LTE system (e.g., using LTE in adynamic and shared spectrum). In one example (e.g., option 1), anetwork, such as a LTE network, may operate using small cells 502 (suchas TVWS Pico cells) that may be restricted to a dynamic and sharedspectrum alone as shown in FIG. 5. Such an example may be adopted orused by new entrants that may not have access to a licensed spectrum.Base stations operating in dynamic and shared spectrum may typically belimited in terms transmitted output power such that cells may likely beof small footprint, for example, a few hundreds of meters in radius.Each base stations may also be linked to a TVWS database at a minimum(e.g., optionally via an O&M entity) and possibly also with acoexistence database.

In an example (e.g., a second option) shown in FIG. 6, a network such asa LTE network may be deployed using small cells 602 operating in dynamicand shared spectrum where an overlay of macro cells using licensedspectrum may also present. Such an example may be viable for an existingoperator that may like or wish to add capacity to network associatedtherewith, offer tiered services, and/or offload capacity to the smallcells 602. Base stations of such networks (e.g., the overlay macro celland the small cells operating in dynamic and shared spectrum) may haveaccess to the TVWS database at a minimum (optionally via an O&M entity)and possibly also with a coexistence database.

An example (e.g., of option 2) with a more sparse deployment of smallcells 702 (e.g., a non-contiguous deployment) may be shown in FIG. 7.

A number of problems may be addressed for base stations operatingentirely in a dynamic and shared spectrum. For example, problemsassociated with the random access procedure for WTRUs camping on suchcells in IDLE mode may be addressed as disclosed herein. The spectrummay be shared by competing secondary users. Such secondary users may usea radio access technology that may be different from LTE. Although someof these radio access technologies may have a built-in coexistencemechanism (e.g., 802.11 systems may rely on carrier sensing multipleaccess (CSMA)), such a co-existence mechanism may not be guaranteed. Asa consequence, a communication system, such as the LTE system, operatingin a dynamic and shared spectrum may be able to deal with bothcontrollable and uncontrollable secondary user interference.Controllable interference may imply that a secondary user may defer itstransmission and allow or enable, for example, LTE to operate free ofsuch secondary user interference. Uncontrollable interference may implythat a secondary user may take no special action to coexist with, forexample, LTE, and the communication system such as the LTE system mayoperate in spite of such secondary user interference. Uncontrollableinterference may be a result of a radio access technology, or it may bealso a result of a layout of a network (e.g., caused by hidden nodes).

The secondary users may cause UL transmission failures as well asdownlink transmission failures, for example, as shown in FIG. 8. Forexample, a secondary user 804 near a base station 802 (e.g., a secondaryuser SU1) may be controllable for DL transmissions from the base station802, but such a secondary user 804 may still result in UL transmissionfailures because the interferer may not be controllable by LTE uplinktransmissions from a WTRU 808 that may be hidden from the secondary user804. Uplink transmissions may be very difficult to receive at the basestation. Similarly, a secondary user 806 near the WTRU 808 (e.g., asecondary user SU2) may be controllable by uplink transmissions from theWTRU 808, but such a secondary user 806 may still result in DLtransmission failures. DL transmissions for the WTRU 808 may bedifficult to receive as the base station 802 may be hidden from thesecondary user 806 as shown in FIG. 8.

In one example, the secondary user may be a WiFi interferer. However, itshould or may be understood that such an example of a potentialsecondary user interference that results in controllable interferencemay be extended to other radio access technologies.

Random access methods or procedures such as RACH methods or proceduresmay need to operate on shared spectrum with secondary users and theequipment used thereby (e.g., secondary WTRUs).

An eNB may support feature detection that may enable the eNB to detectthe presence of a specific secondary user (e.g., WiFi) in an operatingchannel. FIG. 9 illustrates an example method 900 for detecting thepresence of a specific secondary user in an operating channel. At 902,the eNB may use sensing, e.g., feature detection to detect whether aspecific secondary user is present in an operating channel. At 904, theeNB may signal such information to WTRUs, for example, through the useof SIB information or through dedicated signaling such as a RRCconfiguration message. A WTRU may receive this information from the eNBat 906. At 908, the WTRU may be configured based on this information tomodify the RACH procedure 300 of FIG. 3. For example, this may triggerthe WTRU to listen to a communication channel (e.g., a medium) to verifyif the medium may be free prior to sending the preambles as describedherein. Furthermore, the eNB may assist the WTRU by silencing a portionof the downlink subframe, for example, by using an almost blank frame inthe downlink prior to an uplink opportunity for the RACH in the contextof a communication system such as a TDD LTE system or by the absence ofuplink scheduling in the uplink subframe prior to the RACH opportunity.The WTRU may be signaled during such a silencing period by the eNB suchthat the WTRU may do energy detection to detect if other secondary usersmay, in fact, be using the medium or not prior to sensing the RACHpreamble. Accordingly, if a secondary user may be absent in theoperating channel, the WTRU may use a first RACH procedure at a 910. Ifa secondary user may be present in the operating channel, the WTRU mayuse a second RACH procedure at 912.

A WTRU being configured to operate in the presence of a secondary usermay modify the RACH power ramp-up procedure. For example, the WTRU maysend its first preamble at a higher power by a delta from the defaultpower level to be used if an eNB signals the presence of a secondaryuser. Subsequent RACH preamble transmissions may also use the same deltafrom the default power level. The type of secondary user signaled by theeNB, for example, WiFi being present instead of WiMax, may trigger theWTRU to select one of the techniques described herein.

A RACH procedure or method such as that disclosed herein may be enhancedby having a WTRU avoid secondary user interference when transmitting theRACH. The WTRU may perform sensing of a medium with possibly featuredetection to detect the presence of other RATs (e.g., WiFi) to determineif the medium may be available prior to preamble transmission. If themedium may be found to be free, the WTRU may transmit the RACH preamble.Otherwise, the WTRU may wait until the medium may be free and the eNBmay be expecting a RACH preamble to transmit it. As such, the WTRU mayavoid transmitting the RACH preamble at the time when a secondary systemmay also be using the medium and performing unnecessary power rampingthat may eventually interfere with the same communication system such asthe same LTE system or other communication systems such as other LTEsystems operating in the vicinity.

FIG. 10 illustrates a transmission of the RACH using a preliminarysensing or “listen before talk” phase used by a WTRU. For example, aneNB provides RACH preamble resources during uplink subframes. When theMAC layer at the WTRU triggers a RACH, the WTRU may wait for a RACHpreamble resource that may be known to the WTRU via system information.Prior to the start of such a resource, the WTRU may perform a shortsensing of the medium to determine whether the medium may be currentlyused by another secondary user. If the medium may be free, as shown at1002, the WTRU may transmit a preamble 1004 during the RACH resource. Ifthe medium may be busy, the WTRU may perform a retry according to one ormore of a number of rules. If the medium may be busy initially andbecomes free at any time during the resource, as shown at 1006, the WTRUmay transmit a preamble 1008 as long as the transmission may fit intothe current RACH resource. If a medium may be busy during entirepreamble such that if the medium continues to be busy beyond the pointwhere the RACH preamble may be transmitted within the current resource,as shown at 1010, the WTRU may wait until the next available RACHresource and repeat (e.g., transmitting the preamble) without increasingthe power of the preamble. In the event of an unsuccessful RACH suchthat if a WTRU succeeds in transmitting the RACH preamble during a RACHresource and the RACH may not be successful (e.g., no RACH response maybe received from the eNB, or the RACH procedure may fail during thecontention resolution step), the WTRU may repeat (e.g., transmitting thepreamble) after ramping up the transmit power for the RACH preamble.

If multiple consecutive RACH subframes may be available to send thepreambles, the WTRU may sense the medium. If the medium becomes freeduring subframe_x and subframe_x+1 may also be available for RACHpreamble, the WTRU may send a RACH preamble that could terminate insubframe x+1. In other words, the beginning of the RACH preamble may bein subframe x and the end may be in subframe x+1. One rule could be touse the subframe number when constructing the RACH preamble, from whichthe preamble start time belongs. Another rule could be based on thesubframe number from which the preamble start time may be closest to thestart of the subframe.

If multiple consecutive RACH subframes may be available to send thepreambles, if the medium may be busy during an entire RACH subframe, theWTRU may apply power ramp-up rules and may increase the power when itmay send the preamble if the medium may become free in the subsequentsubframe.

A WTRU may perform a sensing procedure to determine whether a medium maybe free or not. The WTRU may modify the power ramp-up rules of the RACHpreambles such that the preambles may be sent at a higher power by adelta from a default power level to be used if the medium may not free.If the medium may be free, the WTRU may follow the default power level.The delta may be signaled by the eNB.

The sensing that may be done prior to sending a RACH preamble mayinvolve a simple energy detection or may involve a feature detection,depending on the type of secondary users expected to coexist with acommunication system, such as the LTE system, and the capabilities ofthe WTRU. For instance, if a LTE system may coexist with other LTEsystems as well as WiFi systems, the LTE system may abstain fromtransmitting the RACH preamble when the channel may be occupied by aWiFi system. Feature detection may be able to detect that a medium maybe busy due to WiFi transmission and not due to LTE transmission. TheeNB may assist the WTRU in determining whether or not other secondaryuser RATs may be present in the channel. For example, SIBs informationmay indicate that a given RAT may be present in the cell, for example,triggering the WTRU to enable feature detection for the specific RAT.

For a small cell, the length of the RACH preamble sequence may also bereduced to increase the length of time in which the Listen Before Talk(LBT) may be performed. The preamble sequence may be long enough toensure unambiguous round-trip estimation time for a WTRU at the edge ofthe largest cell. Since such cells may be limited to 300 m, theapproximate minimum preamble sequence length may be 300/(3×10⁸)=1 μs.Such a minimum may be much shorter than the value of 800 μs for thepreamble sequence in LTE that may be used. The resulting short preamblesequence may then be transmitted once following the LBT time of eachWTRU, or multiple times until the end of the preamble resource to allowfor non-coherent combining of the copies of such a sequence at the eNB.Such repetition may be done a number of times depending on the remainingtime in the RACH subframe at which the WTRU may determine that thechannel may be free of WiFi interference (e.g., a sufficient number ofrepetitions to occupy the remainder of the RACH subframe following asuccessful LBT). FIG. 11 illustrates an example of a variable lengthRACH preamble using sequence repetition. In particular, FIG. 11 depictsa first RACH subframe 1102 having a long LBT 1104 followed by a shortpreamble sequence repetition 1106. FIG. 11 also depicts a second RACHsubframe 1108 having a short LBT 1110 followed by a long preamblesequence repetition 1112.

A short RACH preamble sequence may be transmitted a single time, but ata random time instant by a WTRU to provide a lower probability of RACHcollisions between multiple WTRUs using the same RACH resource. As such,a technique may be used in the context of TDD operation over a smallbandwidth (e.g., typical of TVWS) where an eNB may not allocate as manyRACH resources as in the case of larger bandwidths. This could alsoapply to the case of DL heavy configurations with few uplink subframes,or in the presence of coexistence gaps that may limit the number of ULsubframes in which RACH resources may be allocated by the eNB. To enablethe random transmission of the RACH preamble, the time spent on aninitial LBT that may be performed just prior to the RACH resource may berandomized on a per WTRU basis. A WTRU, when performing LBT, mayinitially spend a random amount of time on the LBT prior to transmissionof the RACH preamble. The WTRU may therefore follow one or more of anumber of rules. FIG. 12 illustrates the use of such rules (e.g., forrandom LBT duration and backoff) using multiple WTRUs. As shown at 1202and 1204, the WTRU may select a random time T_(L) for which to performLBT where T_(L) ranges from T_(min) to T_(max) and where T_(min)corresponds to the amount of time prior to the subframe boundary (at theWTRU) in which to start the LBT, and T_(max) may be specified by the eNBthrough system information. Two different values of T_(L) for twodifferent WTRUs are shown at 1202 and 1204. The WTRU may perform LBT forT_(L) starting T_(min) prior to the subframe boundary and transmit thepreamble immediately after T_(L) when the medium may be found to be freefor the entire time T_(L). If the medium may be found to be occupied,the WTRU may backoff for a specified amount of time, as shown at 1206,and repeat (e.g., performing Listen Before Talk (LBT)) where such abackoff time may also be variable in length.

As multiple WTRUs may send the short preamble in a single subframe, thecurrent definition of RA-RNTI (e.g., the Release 10 definition ofRA-RNTI) may no longer be used at, for example, 304 of the RACHprocedure 300 of FIG. 3 (e.g., to identify the WTRU that may receive thegrant for the L2/L3 message). For example, in a communication system,such as a LTE system, a given preambleID sent in RACH resource y (y=0,1, 2, . . . , 6) in subframe x (x=0, 1, 2, . . . , 9) may beacknowledged by the eNB with a grant to address RA-RNTI=1+x+10y. In theexample shown in FIG. 12, both preambles sent by UE1 and UE2 and shownat 1202 and 1204, respectively, may have the same RA-RNTI. To eliminatesuch confusion, the RA-RNTI may provide an indication of the time atwhich the small preamble may be sent. This indication may be based onthe concept of RACH slots. A RACH subframe may be divided into a numberof RACH slots. The number of slots (N_(slot)) may be equal to thesubframe size divided by the preamble, and potentially cyclic prefix,size. For example, if a RACH preamble+cyclic prefix may be 0.1millisecond in duration, then a 1 millisecond subframe may have 10 RACHslots. The communication system, such as the LTE system, may use alarger preamble set and may reserve distinct preambles for each of theseRACH slots. The WTRU may send consecutive RACH preambles and code theRACH slot or some other identifier (e.g., z) in the combination ofpreambles. The first preamble may still be selected randomly(preambleID1), but the second preamble (preambleID2) may be found bysome combination of preambleID1 and z. For example, one such combinationmay be preambleID2=preambleID1+z. In some cases, the preambleID2 may begiven by (preambleID1+z) mod (the number of preamble IDs). Uponrecovering the set of preambles, the eNB may know the z from thepreambleID combination and then may respond with a grant toRA-RNTI=1+x+10y+60z.

A timing advance may be performed based on an assumption that each WTRUmay transmit the RACH preamble at the beginning of the RACH subframe.Since this may no longer be the case when a RACH preamble may betransmitted using LBT (e.g., as specified above), a procedure may beused for applying timing advance in the WTRU. In particular, the WTRUmay remember the time at which it began transmission of the RACHpreamble. The eNB may, in the random access response, indicate thetiming advance value based on the assumption that the RACH preamble maybe transmitted at the beginning of the subframe. The WTRU may correctthis timing advance command using the knowledge of when it transmittedthe preamble. For example, the correction amount may be the delaybetween the subframe boundary and the preamble transmission both seen bythe WTRU. Subsequently, the WTRU may inform the eNB of the correctionfactor on the timing advance during or after the RRC connection request.

Secondary user interference techniques may rely on the fact that thesecondary user transmissions may defer access to other transmissions ifsuch secondary users may sense the communication resource(carrier/channel) busy. This may be inherent in 802.11-based WiFisystems.

Solutions may be divided into classes. The solutions described may becombined. In a first class, a communication system, such as the LTEsystem, may rely on connected mode WTRUs to guarantee, or almostguarantee, that secondary users may be silent when a random accesstransmission occurs. In a second class, a communication system, such asthe LTE system, may alter the manner in which random accesstransmissions may be sent to increase the probability that secondaryusers may be silent for at least part of the random access transmission.

A random access procedure or method described herein below may also beused or provided. For example, a base station may schedule ULtransmissions on a PUSCH based on coverage area such that ULtransmissions from WTRUs that may be spread across the coverage area.The base station may rely on WTRU location information (e.g., throughGPS reporting or through some network based location information) toschedule WTRUs such that areas of the base station coverage area mayhave at least one WTRU with a scheduled uplink transmission. FIG. 13shows an example where the base station scheduling algorithm may takeinto account the WTRU location by trying to schedule the WTRUs labeledUE(ok) and depicted at 1302. The WTRUs labeled UE(red) and depicted at1304 may be redundant from a coverage perspective. The scheduler mayschedule these but with a lower priority. For fairness, in subsequentsubframes, the scheduler may alternate which WTRUs to schedule. Forexample, the WTRUs shown in the box depicted at 1306 may change roles insubsequent subframes (e.g., a UE(ok) becoming a UE(red) and vice versa).

Ongoing WiFi transmissions may see such a WTRU UL transmission asinterference. Such WiFi transmissions may not be acknowledged and mayuse a retransmission. Such a retransmission may be blocked by the WTRUuplink transmissions. Additionally, other WiFi stations may be waitingfor the medium to become free and may continue to defer theirtransmissions to the WTRU uplink transmissions (see, e.g., FIG. 14).

A base station may schedule a RACH in subframes where the LTE system maybe likely to have no secondary user interference. In FIG. 14, this mayoccur in subframes 1402 labeled UL/RACH. The location of these UL/RACHsubframes 1402 may depend on the type of secondary user interferencethat the LTE system may be trying to control. For example, this maydepend on the largest WiFi frame size.

A random access procedure or method described herein below may also beused or provided. For example, the base station may rely on the UpPTS tocancel any ongoing WiFi transmissions. The role of the UpPTS may bealtered to send a form of strong jamming signal to the WiFitransmissions. Frame transmissions that may overlap the UpPTS may likelyfail and result in a retransmission after the appropriate delay forreception of the WiFi ACK, the interframe spacing, and the randomcontention window. During such an interval, the LTE system may schedulea random access transmission in an UL subframe. The UL subframe tochoose may be based on the type of secondary user interference that theLTE system may be trying to control. For example, this may depend on thelargest WiFi frame size. The transmitted UpPTS signal may bepre-configured in the WTRU, or obtained through system information. EachWTRU may send such a signal during the UpPTS portion of a special orparticular subframe.

A random access procedure or method described herein below may also beused or provided. For example, the LTE system may rely on a type ofspecial subframe to cancel ongoing WiFi transmissions. Such a specialsubframe (hereinafter referred to as a Clear (C) subframe) may betransmitted by connected mode WTRUs. FIG. 15 illustrates an example ofWTRU transmissions during a C subframe. During such a subframe, the WTRUmay randomly choose one or more resource blocks 1502 and may transmit aspecial packet. Resource blocks 1502 may be available for the specialpacket. A subset of the resource blocks 1502 may be available for thespecial packet. As connected mode WTRUs may be transmitting on theuplink, this may cause any frame transmissions that may overlap the Csubframe to likely fail, resulting in a retransmission after theappropriate delay (e.g., delay due to reception of the WiFi ACK, theinterframe spacing, and the random contention window). During such aninterval, the LTE system may set aside UL subframes to carry randomaccess transmissions.

A random access procedure or method described herein below may also beused or provided. For example, the LTE system may reserve a portion ofthe resource to carry a busy indication. As illustrated in FIG. 16, thereserved resource may be a set 1602 of subcarriers that may carry a busysignal, or a set 1604 of resource blocks that carry a busy PDU.Connected mode WTRUs may transmit such a busy indication according to aspecific frequency (e.g., once every K uplink subframes). The value of Kas well as the transmit power for the indication may be preconfigured orprovided through RRC signaling (e.g., through system information). Thelocation of the busy indication may be close to the extremities of theband to be closer to the PUCCH and avoid non-contiguous uplinktransmissions.

A random access procedure or method described herein below may also beused or provided. For example, a random access transmission may beextended to provide enough time for a secondary user to allowtransmitting stations to complete their frame transmission (e.g., ifany), sense the medium as busy, and/or defer, and/or may allow alreadydeferring stations to continue to sense the medium as busy and defer.The random access transmission may be extended by using a long preambleformat, e.g., either an existing format or a new format). For example,FIG. 17 shows an example format 1700 spread over a random accesstransmit window of 3 milliseconds where a short cyclic prefix 1702 (sizeT_(CP)) may be followed by a preamble 1704 of size T_(seq) that may berepeated multiple times, e.g., three times. Optionally, the cyclicprefix 1702 may be repeated between each repetition. A WTRU 1706 maytransmit the same preamble in each repetition and at the same power. TheWTRU 1706 may ramp up the power for each retransmission. The example inFIG. 17 shows a secondary user 1 (SU1) frame 1708 colliding with thefirst two preamble transmissions. However, the random accesstransmissions may act as interference to this frame resulting, forexample, in a failed transmission. When SU1 may try to retransmit, themedium may be busy carrying the repeated preamble sequence. Both theWTRU 1706 and a base station 1710 may know the size of the random accesstransmit window. Such a window may be sized based on the type ofsecondary user interference that the LTE system may be trying tocontrol. For example, this may depend on the largest WiFi frame size.

A random access procedure or method described herein below may also beused or provided. For example, repeated transmissions may benon-continuous. FIG. 18 shows an example of repeated random accesstransmission that may be non-continuous. For example, each transmissionmay be within a single subframe. The interval between retransmissionsmay prevent secondary users from acquiring a medium (e.g., if thesecondary user may be WiFi, the interval may be less than DCFinter-frame spacing). A format may be provided that may repeat a randomaccess transmission K times, where each transmission may have the samepreamble 1802 of duration T_(seq) and may be preceded with its owncyclic prefix 1804 of size T_(CP). The transmissions may be inconsecutive subframes or every N subframes where N may be determinedbased on the type of secondary user interference.

A random access procedure or method described herein below may also beused or provided. For example, the communication system may alter themanner in which random access transmissions may be sent such that theprobability that secondary users may be silent for at least part of therandom access transmission may be increased. A WTRU and base station maybe aware of one or more of the following: a size of the random accesstransmission window; the LTE resource blocks reserved for the randomaccess transmissions; the timing of the random access transmissionwindow (e.g., the specific subframes and the frequency at which such arandom access transmission window repeats); the details of the preambleformat, the number of repetitions (K); the available preambles; thetransmit power for the preambles; and/or any other random access relatedparameters.

In such a random access procedure or method 1900 as depicted in FIG. 19,at 1902, a WTRU may randomly select a preamble (e.g., from thoseavailable) and may randomly select a random access transmission window.The WTRU may select the next available window. The WTRU may determinethe transit power to use for the preamble transmissions and may send thepreamble ID of the selected preamble K times (e.g., using eithercontinuous or non-continuous repeated random access transmission asshown in FIG. 17 or FIG. 18, respectively). The same preambleID may berepeated in each of the transmissions at the same transmit power. TheWTRU may ramp up the power for each retransmission.

Then, at 1904, a base station (e.g., an eNB) may search for thepreambles in the random access transmission window. The base station oreNB may find the preamble in any of the K transmissions. The eNB maywait 2-3 subframes after the end of the random access transmissionwindow to schedule a RACH message. This RACH message may include thefound or determined preamble ID, a temporary C-RNTI, a timing adjustmentmessage, and/or an uplink grant. At the same time, the WTRU may open upits random access response window a few subframes after the end of therandom access transmission window looking for the RA-RNTI and a matchingpreambleID. The RA-RNTI may use the formula RA-RNTI=1+t_id+10*f_id,where t_id may be the last subframe of the random access transmissionwindow (0, 1, 2, 3, . . . , 9) and f_id may be the frequency index ofthe random access block used for the random access transmission (0, 1,2, 3, 4, 5).

The random access procedure or method 1900 may then proceed similarly to306 and 308 as described herein above in connection with FIG. 3. Forexample, at 1906, the WTRU may use an UL grant to send an uplinktransmission on PUSCH. At 1908, the WTRU may perform contentionresolution.

If the preamble transmissions may be unsuccessful, the WTRU may ramp upthe transmit power of the preamble and may try again (e.g., as definedin Release 10) with the exception that the retry may again be atransmission of repeated preambles (e.g., using either continuous ornon-continuous repeated random access transmission as shown in FIG. 17or FIG. 18, respectively).

Since the preamble may be repeated K times in each random accesstransmission window, the base station may use such knowledge todetermine that more than one WTRU may have selected the same preamble ina random access resource. If multiple WTRUs transmit the same preamblein the same RACH resource, the resulting collision may not be detectableat 1904 above. Such a collision may be resolved through contentionresolution. In the second class of solutions in which the communicationsystem may alter the manner in which random access transmissions may besent to increase the probability that secondary users may be silent forat least part of the random access transmission, where the preamble maybe repeated K times, the base station may detect the collision at 1904and may take a preventative action. The base station may also try tocorrelate the preambles across the random access transmission window.During such a window, the base station may detect none, one, or up to Kpreambles (e.g., for each of the preamble transmissions). The basestation may detect a collision (e.g., two WTRUs having selected the samepreamble and transmitted in the same random access resource) byobserving different timing adjustments across the random accesstransmission window and/or an odd preamble correlation pattern. Forexample, a base station may determine that a preamble may be received insub frame k+0 and k+2 and a missing preamble in subframe k+1 may suggestthat the preambles in subframe k+0 and k+2 may be from different WTRUs.

An eNB or base station may resolve the contention by asking the WTRUs totry again at the next window. As such, at 1904, the eNB may respond tothe WTRUs on the RA-RNTI (or a RNTI) informing such WTRUs that acollision may have occurred and to retry at a future random accesstransmission window. Such an attempt may be performed without a powerramp-up and without incrementing the count on the number of randomaccess attempts. At 1904, the eNB may respond on the RA-RNTI withmultiple grants (e.g., one for each discerned preamble). Each grant mayhave its own temporary C-RNTI and timing adjustment. After receiving thetwo grants, the colliding WTRUs may randomly select one of them (e.g.,grants) for transmission of their message, e.g., at 1906. This messagemay be successful if the WTRU may select the grant that may have thecorrect timing adjustment.

Preamble sizes used in solutions herein may be similar to, for example,preamble sizes included in LTE Release 10. The solutions describedherein may be extended to smaller preamble sizes. Furthermore, thesolutions described herein may be readily combined with sensingsolutions. For example, in a system where the preamble may be repeated Ktimes, the WTRU may sense a medium after every L transmissions of thepreamble (L<K). The sensing may be simple energy detection for a veryshort period of time. If the medium may be sensed free, the WTRU mayproceed with N more retransmissions of the preamble where N may be assmall as 1. If the medium may be sensed busy, the WTRU may try with anadditional L retransmissions and may then sense again. After the mediummay be sensed free, there may be no more secondary user interference andthe WTRU may send a few RACH preambles. The WTRU may transmit fewer thanK preambles, which may result in less interference to random accesstransmissions from other WTRUs.

A RACH procedure may be configured to cooperate with a coexistencemechanism, for example, a subframe-based coexistence mechanism. A WTRUmay not be aware of one or more associated coexistence gap periods. AneNB may select PRACH resources and/or a RACH response window for one ormore WTRUs based on knowledge of the coexistence gap.

The eNB may obtain the coexistence gap information, for example, from ascheduler. The eNB may use the coexistence gap information to choose aPRACH and/or RACH configuration, for example by selecting a“prach-ConfigIndex” and/or RACH response window size(“ra-ResponseWindowSize”). The eNB may send the selectedprach-ConfigIndex and/or the selected ra-ResponseWindowSize, for examplewith an SIB2 message.

FIG. 20 depicts an example Time-Division Duplex (TDD) frame 2000. Forexample, the eNB may select a prach-ConfigIndex such that the WTRUselects subframe 2, depicted at 2002, for preamble transmission. Theselected index may avoid subframe 7, depicted at 2004, for example.

One or more WTRUs may read the prach-ConfigIndex. Based, for example, onone or more restrictions indicated in the prach-ConfigIndex, a subframecontaining PRACH (e.g., a next available subframe containing PRACH) maybe selected for preamble transmission. For example, subframe 2, depictedat 2002, may be selected for preamble transmission.

The eNB may select a ra-ResponseWindowSize to compensate for a gapperiod, for example, by increasing the window size in accordance with asize of an OFF gap period. The WTRU may listen for the response duringthe gap period and/or beyond the gap period.

If the coexistence gap period changes, the eNB may select a differentPRACH configuration, for example, by selecting a differentprach-ConfigIndex and/or ra-ResponseWindowSize. The selectedprach-ConfigIndex and/or ra-ResponseWindowSize may comprise an IE thatmay be sent with an updated SIB2, for example. For example, a SIB2 maybe changed in accordance with 160 millisecond intervals and/or may berepeated in accordance with 20 or 40 millisecond intervals.

Information pertaining to the different PRACH configuration may be sentvia physical layer (e.g., Layer 1) signaling of “PRACH resources” and/or“RA Response Window Size” by an eNB. For example, a WTRU may wake up inaccordance with one or more DRX cycles and may read one or moresynchronization signals, for example a Primary Synchronization Signal(PSS) and/or a Secondary Synchronization Signal (SSS). A relativeposition of the PSS and/or the SSS may be used to indicate PRACHresources. The position of the reference signal may be unique in a celland may be related to a Cell ID. For example, cell-specific ReferenceSignals (RSs) may be provided for 1, 2, and/or 4 antenna ports. Sixcell-specific frequency shifts may be configured. RS positions may beused as an indication of PRACH resources.

Information pertaining to the different PRACH configuration may be sentin accordance with a SIB2 scheduled transmission change. For example, aneNB may change the PRACH information in the SIB2 when it is repeated inaccordance with 20 millisecond intervals. The eNB may send an “SI changeindication” with the MIB that may indicate that the PRACH informationhas changed and that the WTRU may limit reading of the SIB2 to one ormore portions pertaining to the PRACH information. For example, a WTRUmay wake up during a DRX ON period and, if the SIB2 change indication ispresent, may read the PRACH information.

A RACH procedure may be configured to cooperate with a coexistencemechanism, for example, a subframe-based coexistence mechanism. A WTRUmay be aware of one or more associated coexistence gap periods. Forexample, a WTRU may be made aware of one or more configurationspertaining to the RACH procedure and/or coexistence mechanism. Inaddition to the co-existence mechanism, there may be one or more silentperiods, for example due to eNB Discontinuous Transmission (DTX) forpower savings. The WTRU may be configured to decide how to coordinatebetween the RACH procedure and/or coexistence mechanism, for example.

The example TDD frame structure and configuration depicted in FIG. 20,having a gap off period 2006 of five subframes, may be used. FIG. 21depicts an example information exchange between a WTRU 2102 and an eNB2104 that may be implemented to coordinate a RACH and a coexistencemechanism.

A WTRU may be made aware of one or more coexistence gap patterns, forinstance using broadcast messages and/or PHY signaling. For example, aWTRU may know which subframes in the configuration shown in FIG. 20 areOn and which subframes are Off. As depicted in FIG. 20, subframes 0, 1,and 2 are On, subframes 3, 4, 5, 6, and 7 are Off, and subframes 8 and 9are On. This pattern may produce a fifty percent (50%) duty cycle. TheWTRU may store the subframe-based gap patterns at 2106 of FIG. 21.

One or more WTRUs may know about the available PRACH resources (e.g., ULsubframes 2 and 7 depicted in FIG. 20 have allocated PRACH resources)using a mechanism such as a “prachConfiguration Index” sent in an SIB2,for example.

A WTRU may first select a subset of PRACH resources, which may not fallin the gap, from the available PRACH resources. The WTRU may selectPRACH resources in subframe 2, for example. If there are multipleresources in subframe 2, the WTRU may randomly select a PRACH resourcefrom the subset of PRACH resources for preamble transmission at 2108 ofFIG. 21. The WTRU may also select a PRACH opportunity in a next frame,for example to avoid collision probability.

The WTRU may obtain an “RA Response” window size from the eNB. Based onthe gap information, the WTRU may take one or more of the followingactions. The WTRU may wait to start a response window until a nextavailable DL subframe outside of an OFF period. For example, inaccordance with the illustrated example, as illustrated in FIG. 20 andat 2110 of FIG. 21, the WTRU may wait 5 (=3+2) subframes, before itstarts the response window. The WTRU may extend the RA Response windowso that it includes the OFF period. The WTRU may monitor a responsewindow that may be split across multiple frames. The response window maybe limited to subframes that are DL subframes, for example subframes 0and 1.

The eNB may halt its activity during the OFF period and may resume fromwhere it left during a subsequent ON period. The WTRU may not inform theeNB about the extended RA Response Window size.

If the WTRU is unable to find PRACH resources outside the coexistencegap OFF periods for N consecutive number of subframes, it may attemptcell reselection. As part of the cell reselection procedure, the WTRUmay monitor the availability of PRACH resources and may initiate a cellreselection if this availability falls below a threshold. PRACH resourceavailability may be measured by monitoring the number of PRACHopportunities in a moving window, for example.

A RACH procedure may need to integrate with a “transparent frame” basedCoexistence Mechanism. For example, coexistence gaps may be introducedwith a minimal impact on HARQ and/or other transmission timing rules bycausing the coexistence gaps to span an integer number of frames.Because the TDD UL/DL configuration may be repeated (e.g., in eachframe), in accordance with a gap that spans substantially the entiretyof a frame, the timing and/or rules of the TDD HARQ may be adapted insuch a way that one or more timings (e.g., all timings) may be skewed byan integer number of frames.

The WTRU may be made aware about the configurations of the RACHprocedure and/or the transparent frame information for coexistence gaps.The PRACH resource selection may involve a two-part process, for exampleselection within a frame and then selection of a frame. The WTRU mayselect PRACH resources within a frame based on information sent by eNB.The same PRACH resources may be available in one or more frames (e.g.,in every frame). The WTRU may then select a frame (e.g., randomly) fromthe frames in which transmission is allowed (e.g., not a transparentframe), to send the RACH preamble. The selection may be limited to thenext K frames where transmission is allowed, for example. The WTRU mayre-evaluate a path loss parameter for one or more RACH retransmissions(e.g., for each RACH retransmission).

The WTRU may obtain an “RA Response” window size from an associated eNB.After sending the RACH preamble and four subsequent subframes, forexample, the WTRU may start counting the “RA Response” window. If thewindow extends to the next frame, which may be a transparent frame, theWTRU may take one or more of the following actions. The WTRU may stopcounting the window for the complete “transparent frame.” Once the frameis over, the WTRU may restart the counter. The WTRU may extend the RAResponse window so that it includes the total “transparent frame”period. The WTRU may start the RA Response window at a next frame inwhich transmission is allowed.

The eNB may halt its activity during the OFF period and may resume fromwhere it left during the ON period. The WTRU may not inform the eNBabout the extended RA Response Window size.

An eNB may be configured to modify a RACH capacity. For example, an eNBmay monitor the PRACH resources remaining after one or more coexistencegap OFF periods. If the available PRACH resources are low, the eNB mayincrease the number of PRACH resources. The eNB may maintain a constantaverage number of resources over a given time period. For example, inaccordance with frame structure type 2 with preamble formats 0-4, theremay be multiple random access resources in an UL subframe (or UpPTS forpreamble format 4) depending on the UL/DL configuration, for example.There may be a maximum of 6 PRACH resources, which may correspond to 36(6×6) resource blocks in a subframe and/or 0≦f_id<6. When asubframe-based coexistence gap is introduced, the eNB may increaseallocation of PRACH resources in a subframe (e.g., from 6 to 12 resourceblocks) if UL frames are lost to coexistence gap periods, for example.

A communication system, such as a standalone LTE TVWS system, mayoperate in an environment where there may be various sources ofinterference. Such sources of interferences may include primary users,such as DTV and/or microphone users, and/or secondary users, such asWiFi, LTE system users, and the like. According to an example, WTRUs maycamp on a single cell after powering up, e.g., using a LTE Release 10procedure. The cell may be crowded with other LTE systems and secondaryusers generating significant co-channel interference. As such, initialaccess for WTRUs using the RACH procedure may use a large number ofattempts compared to a licensed band operation, such that the overall“initial access” time for WTRUs in an LTE TVWS system may increase.

For carrier aggregation (CA) capable WTRUs, the probability of asuccessful random access attempt may be increased if the random accessmay be attempted in more than one carrier frequency. If the WTRUs maysuccessfully complete the RACH procedure with fewer attempts, then suchWTRUs may get access faster than WTRUs without CA capability in LTE TVWSsystem.

Additionally, when a WTRU may be switched on, the WTRU may scan RFchannels in the specified bands according to its capabilities to findavailable PLMNs. On each carrier frequency, the WTRU may look for thestrongest cell and read its system information. Using the systeminformation, the WTRU may find out which PLMN(s) the cell belongs to. Ifthe WTRU may read one or several PLMN identities in the strongest cell,each PLMN (e.g., found PLMN) may be reported to a NAS. The NAS mayselect a suitable PLMN from a list. Once the WTRU has selected a PLMN,the cell selection procedure may be performed to select a suitable cellfor the PLMN to camp on. The WTRU may further select a suitable cellbased on idle mode measurements and cell selection criteria.

According to additional examples, CA capable WTRUs may transmit andreceive simultaneously in two different channels. Thus, instead ofcamping on one cell, the WTRU may select more than one cell from thelist of measured cells. Additionally, the WTRU may choose the highestranking N number of cells from the list. N may be in a range of 1<N<6(e.g., since the maximum number of carriers for aggregation may berestricted to 5).

As shown in FIG. 22, a WTRU 2202 may camp on two cells on two differentcarrier frequencies 2204 and 2206. The WTRU 2202 may read the “Broadcastinformation (SIB2)” on both of the cells and may get the informationabout the available PRACH resources on each of the cells. The two cellsmay belong to the same eNodeB 2208 or may be from two different eNodeBs.After the WTRU 2202 may successfully camp on two cells, the WTRU 2202may start a RACH procedure on both of the cells.

To start the RACH procedure (e.g., at 302 of the RACH procedure 300 ofFIG. 3), a WTRU may select a RACH preamble for both carriers, e.g.,cells 2302 and 2304 of FIG. 23. In the broadcast information of eachcell, the WTRU may be signaled two subsets 2306 and 2308 that mayinclude 64 preambles as shown in FIG. 23.

A WTRU may also choose randomly a single preamble to be used over bothcarriers (e.g., since the L3 message size is the same) and/or twodifferent RACH preambles that may be used over two different carriers(e.g., at 302 of the RACH procedure 300 of FIG. 3).

Format information may then be sent in the broadcast information (e.g.,as part of 302 of the RACH procedure 300 of FIG. 3). The base station oreNB may request to use the same format information on both carriers. Ifthe two carriers are from two different sites, then the format may bedifferent. The WTRU may also determine the power to be used for thepreamble transmission on both carriers. The WTRU may further select thePRACH opportunity for both carriers. An eNB or base station may designthe PRACH resources in the two cells in such that the cells may beseparated in time as shown in FIG. 24. FIG. 24 illustrates two cells2402 and 2404 having PRACH resources 2406 separated in time between thetwo cells 2402 and 2404.

A WTRU may send a preamble on cell 2402 and then send the preamble oncell 2404. The MAC layer may coordinate to make sure that theopportunities chosen may have sufficient time separation, e.g., if PRACHin subframe 1 may be chosen for cell 2402, then for cell 2404, it may bebetter to choose subframe 6 for preamble transmission. The probabilityof avoiding secondary user interference may increase. Additionally, thepreamble transmission may include different RA-RNTI on the two cells.

A WTRU may sense the channel on cell 2402. If the channel may beavailable, then the WTRU may send the preamble on cell 2402 and may notattempt to send the preamble again on cell 2404. If the channel may notbe available, then the WTRU may wait and send the preamble in the nextopportunity on cell 2404.

FIG. 25 illustrates two cells 2502 and 2504 that may have PRACHresources 2506 that may not be separated in time. If the PRACH resources2506 may not be separate in the time domain for both the cells 2502 and2504 as shown in FIG. 25, then the WTRU may choose to transmit thepreamble within the same time opportunity (e.g., also at 302 of the RACHprocedure 300 of FIG. 3). The WTRU may use same RA-RNTI in such anexample.

The WTRU may then start monitoring the PDCCH on both the carriers suchthat the WTRU may get RA response within the “RA Response Window” timeframe (e.g., at 302 of the RACH procedure 300 of FIG. 3).

An eNB may successfully receive the RACH preamble from both the carriersor from either one of the carriers (e.g., at 304 of the RACH procedure300 of FIG. 3). For example, an eNB may be able to successfully receivethe RACH preamble from both the carriers (F1 and F2, e.g., cells 2502and 2504 of FIG. 25) and depending on the link condition, it may chooseto send the RA Response on the better link between the two links (F1 orF2). Additionally, an eNB may be able to successfully receive the RACHpreamble on one carrier (e.g., F1) where the link condition of thatcarrier (e.g., F1) may be good and the WTRU may send the RA response onthat carrier (e.g., F1). An eNB may be able to successfully receive theRACH preamble on one carrier (e.g., F1) where the link condition of thatcarrier (e.g., F1) may not be good and the WTRU may send the RA responseon another carrier (e.g., F2).

According to an example, different RA-RNTIs may be used by the WTRU ontwo cells. For example, RA-RNTI-1 may be sent on carrier F1, e.g., cell2502 of FIG. 25, and RA-RNTI-2 may be sent on carrier F2, e.g., cell2504 of FIG. 25. The WTRU may receive RA-RNTI-1 on cell 2504 orRA-RNTI-2 on cell 2502. To handle such examples, the WTRU may listen forthe two RA-RNTIs (e.g., RA-RNT-1 & RA-RNTI-2) on a PDCCH of bothcarriers (e.g., cells 2502 and 2504 of FIG. 25). If different preambleIDs may be used, a WTRU may match against the two preamble IDs (e.g.,after RA-RNTI decoding).

Based on the examples described above and the RACH opportunity selectedby the WTRU for preamble transmission, an eNB and the WTRU may have tohandle one out of four possible combinations of RA-RNTI and Preamble Idon the two cells (e.g., F1 and F2, or cells 2502 and 2504 of FIG. 25)including: same RA-RNTI, same Preamble ID; same RA-RNTI, differentPreamble ID; different RA-RNTI, same Preamble ID; and/or differentRA-RNTI, different Preamble ID.

Based on the outcome of RA-RNTI search and Preamble ID matching, theWTRU may know which carrier the UL grant and the timing advance commandto be used (e.g., at 304 of the RACH procedure 300 of FIG. 3). Forexample, the WTRU may receive a RA-RESPONSE with RA-RNTI-1 on carrier F2(e.g., cell 2504 of FIG. 25), may be able to process the message, andmay know that the “UL grant” and the “timing advance” command may haveto be applied on carrier F1 (e.g., cell 2502 of FIG. 25). The WTRU mayattempt to apply the timing advance command on carrier F1 and processthe UL grant for carrier F1. Subsequently, carrier F1 may be made thePrimary Component Carrier (PCC) by the WTRU. Additionally, the WTRU mayassume the RACH procedure to be successful and may terminate the RACHprocedure on carrier F2 such that operations on carrier F2 may be shutdown and the WTRU may go back to the state where it is camping on asingle cell.

According to an example, the contention resolution process may thencontinue on carrier F1. The procedure may then continue as per 306 and308 of the RACH procedure 300 of FIG. 3.

A WTRU may be allocated a certain Transmit Power level per 100 m-by-100m pixel area (e.g., under OFCOM for TVWS). Such an allocation may affecta RACH, because a mobile device (e.g., a WTRU or other component of acommunication system) that wants to access a TVWS channel may have toassume a conservative “safe” transmission power until it receivesinformation about the power limit at its current pixel.

An eNB may broadcast the power allocation information and the mobiledevice (e.g., a WTRU or other component of a communication system) mayuse its own geo-location capability to determine the correct transmitpower. A mobile device (e.g., a WTRU or other component of acommunication system) may submit its geo-location information to theeNB, using a minimum safe transmit power and then may receive its powerallocation in a base station response. Such solutions may be describedin more detail below.

For example, as shown in FIG. 26, an eNB 2602 may broadcast the transmit(Tx) power limits for each pixel. Such information may be carried in thesystem information (e.g., system information blocks (SIB)) and may bebroadcast for reception by a WTRU 2604 attempting to access the networkor attempting to validate its transmit power allocation information.After reception of the system information (e.g., SIBs), the WTRU 2604may know what power level to transmit at in its current location.

Variations in this example may also be provided and/or used. Forexample, the system information (e.g., SIB) may include the transmitpower limit for every pixel within its coverage area along with Latitudeand Longitude of each pixel and bits to distinguish the available powerlevels. The eNB 2602 may broadcast its own location information in theform of Latitude and Longitude. To save bits, the eNB 2602 may alsotransmit the location information of each pixel in terms of relativeposition. Although pixel locations may be absolute, for example, interms of latitude and longitude, it may be easier to express them interms of relative position to save bits. Additionally, the locationinformation may be in polar coordinates in the form (longitude offset,latitude offset), for example (2,2) may indicate or mean 2 pixels northand 2 pixels east of a base station. Such methods may or may not be usedwith circular coverage area around the base station. As such, usingpolar coordinates or any other radial method may be used to indicate therelative location in fewer bits.

To save system information (e.g., SIB) resources, the system information(e.g., SIB) may include the worst-case transmit power limit for a subsetof all pixels in the cell. A pixel subset may be defined by quadrant(e.g., a range of all pixels directly east to all pixels directly northfor example), by radius (e.g., a range of all pixels from 100 m to 200 mfor example), or a subset may be the whole cell. The WTRU 2604 may thenbegin the RACH procedure using such a worst-case power limit. When theWTRU 2604 may have the option to connect to multiple cells, the WTRU mayprefer the cell with the higher worst-case transmit power limit.

As shown in FIG. 27, a mobile device 2702 (e.g., a WTRU or othercomponent of a communication system) may submit its geo-locationinformation to an eNB 2704 using a minimum safe transmit power and thenmay receive its power allocation in response. Such an implementation maybe well suited for cases where the RACH preamble may recoverable at theeNBs, at a power lower than that that may be used for PDU transmission.This may be used, for example, where the preamble transmission may bemade very robust.

For example, a WTRU may encode its pixel location in the Random AccessPreamble. The WTRU may encode a random 6-bit WTRU ID message that may bestaggered in the RACH channel space (e.g., in LTE Release 10). Theavailable combinations of channel staggering may encode the RA-RNTI.Such bits may be modified to identify the pixel locations relative to abase station (or eNB). This modification may not break the random accesspurpose of such bits, as WTRUs in different pixels may still be sendingdifferent bits. Within the same pixel, the staggering may be used foradditional random access.

Additionally, a calculation of an estimated number of pixels per cellmay be used to determine or calculate how many bits may be used forpixel indication. For example, pixels of 100×100 m squares may be used(e.g., as defined by OFCOM). Based on the coverage radius of the cell,the number of pixels per cell may be estimated. For example, in apicocell with a radius of 300 m, the approximate number of pixels may becalculated as follows: Area of Cell/Area of Pixel=(3.14·300·300 m² percell)/(100·100 m² per pixel)=28.26 pixels. The geometry of the pixelsmeshing with the geometry of the picocell may also be provided or used.Additionally, there may be a few corners at the edge of the cell thatmay not be covered by the 30 pixels from such calculation and five bitsmay be used to encode 32 different possible pixel locations.

As such, for a picocell, five bits may encode the pixel location, and asixth bit may indicate that the WTRU resides in a corner case. Thestaggering combinations may then be used for random access purposeswithin each pixel.

The pixel information may be encoded using specific combinations ofconsecutive preamble transmissions (e.g., as shown in FIG. 28 between aWTRU 2802 and an eNB 2804) where each combination of preambles maycorrespond to a specific pixel.

As shown in FIG. 29, a WTRU 2902 may encode the pixel locationinformation within an L2/L3 message shown at 2904 that may be sent to aneNB 2906. For example, in current solutions, WTRUs from the same pixelmay use the same initial identity. However, in some cases (e.g., such ascars coming out of a tunnel), it may not be possible for performancereasons. As such, the geo-location information may be sent on the L2/L3message.

As shown in FIG. 30, depending on the context of the L2/L3 message(e.g., RRC connection request, TA update, scheduling request, and thelike), there may not be enough space on a PUSCH resource that may beallocated for the L2/L3 message. A message, such as a new message, maybe sent that may hijack the L2/L3 uplink resource for the purpose oftransmitting the location data to the eNB. Since a WTRU 3002 may sufferfrom a robustness issue on the UL-SCH, the WTRU 3002 may transmitmultiple copies of the location data over the uplink allocation. An eNB3004 may recognize the pixel location message and may respond with agrant for another uplink resource for the L2/L3 along with the transmitpower limit. Such a grant or information may be sent in the form of asecond Random-Access Response except with transmit power limitinformation instead of timing adjustment information. If other WTRUs maybe in contention, the eNB 3004 may decide to resolve the contention forthe other WTRUs first. The first WTRU 3002 may then restart the processby sending a new RA preamble.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element may be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, WTRU, terminal, base station, RNC, or any host computer.Features and/or elements described herein with reference to an eNB oreNodeB and/or a WTRU or WTRU may not be limited thereto and may beimplemented using any suitable components of a communication system, forexample an LTE system.

What is claimed:
 1. A method for configuring a random access channel(RACH) procedure used by a wireless transmit/receive unit (WTRU) in acommunication system, the method comprising: determining whether asecondary user is present in an operating channel; and performing a RACHprocedure based on the determination, wherein based on a determinationthat the secondary user is absent in the operating channel of thecommunication system, a first RACH procedure is performed, and based ona determination that the secondary user is present in the operatingchannel of the communication system, a second RACH procedure differentfrom the first RACH procedure is performed.
 2. The method of claim 1,wherein the second RACH procedure is based on a type of the secondaryuser.
 3. The method of claim 1, wherein the second RACH procedure isconfigured by an eNB.
 4. The method of claim 1, further comprisingreceiving information relating to whether the secondary user is presentin the operating channel, wherein the determining is based on thereceived information.
 5. The method of claim 4, wherein the informationrelating to whether the secondary user is present in the operatingchannel is received from an eNB, and the eNB uses a feature detection todetermine whether the secondary user is present in the operatingchannel.
 6. The method of claim 4, wherein the information relating towhether the secondary user is present or absent in the operating channelof the communication system is received via an RRC configurationmessage.
 7. The method of claim 1, wherein the WTRU sends a preamble ata power level higher than a default power level if the secondary user ispresent in the operating channel of the communication system.
 8. Amethod for sending a random access channel (RACH) from a wirelesstransmit/receive unit (WTRU), the method comprising: determining whethera communication channel is available during a RACH resource based onsensing on the communication channel; and determining a timing forsending a RACH preamble based on whether the communication channel isavailable during the RACH resource, wherein the RACH preamble isdetermined to be sent during the RACH resource when the communicationchannel is available during the RACH resource, and the RACH preamble isdetermined to be sent during a subsequent RACH resource when thecommunication channel is unavailable during the RACH resource.
 9. Themethod of claim 8, further comprising sending the RACH preamble from theWTRU during an immediately subsequent RACH resource without increasing apower of the RACH preamble when the communication channel is unavailableduring the RACH resource.
 10. The method of claim 8, further comprisingsending the RACH preamble from the WTRU during an immediately subsequentRACH resource with an increased power during the subsequent RACHresource when the communication channel is unavailable during the RACHresource.
 11. The method of claim 8, further comprising sending the RACHpreamble over multiple consecutive RACH resources when the multipleconsecutive RACH resources are available.
 12. The method of claim 8,further comprising when multiple consecutive RACH resources areavailable and the communication channel is unavailable during an entireRACH resource, sending the RACH preamble with an increased power duringthe subsequent RACH resource of the multiple consecutive RACH resources.13. The method of claim 8, further comprising: adjusting power level forsending the RACH preamble based on whether the communication channel isavailable, wherein a default power level is used when the communicationchannel is available, and an increased power relative to the defaultpower level is used when the communication channel is unavailable. 14.The method of claim 8, further comprising sensing the communicationchannel by performing at least one of an energy detection or a featuredetection.
 15. The method of claim 14, wherein the feature detection isused to determine whether the communication channel is occupied by aWiFi system, the method further comprising sending the RACH preamblewhen the communication channel is not occupied by the WiFi system. 16.The method of claim 8, further comprising reducing a length of the RACHpreamble.
 17. The method of claim 16, further comprising sending thereduced-length RACH preamble once following a Listen Before Talk (LBT)time of the WTRU.
 18. The method of claim 16, further comprising sendingthe reduced-length RACH preamble multiple times before an end of theRACH resource.
 19. The method of claim 16, further comprising sendingthe reduced-length RACH preamble once at a random time during the RACHresource.
 20. The method of claim 19, wherein sending the reduced-lengthRACH preamble once at a random time during the RACH resource comprises:selecting a random time for the WTRU to perform a Listen Before Talk(LBT) procedure; and performing the LBT procedure the selected time andsending the RACH preamble based on whether the communication channel isavailable, wherein, the RACH preamble is sent when the communicationchannel is available for the entire time of the LBT procedure, and theLBT procedure is repeated when the communication channel is unavailableduring the LBT procedure.
 21. A method for using a communication systemcomprising a wireless transmit/receive unit (WTRU) in a spectrum, themethod comprising: selecting a random access channel (RACH) procedure asa function of a presence or an absence of a secondary user in anoperating channel of the communication system; and performing theselected random access channel (RACH) procedure.
 22. The method of claim21, further comprising configuring the RACH procedure to reducesecondary interference.
 23. The method of claim 21, wherein performingthe selected RACH procedure comprises sending at least one of a RACHpreamble and format information.
 24. The method of claim 23, whereinperforming the selected RACH procedure comprises determining atransmission power for at least one of the RACH preamble and the formatinformation.
 25. A method for configuring a random access channel (RACH)procedure used by a wireless transmit/receive unit (WTRU) in acommunication system, the method comprising: determining, at an eNB,whether a secondary user is present in an operating channel of thecommunication system; and configuring the RACH procedure at the WTRUbased on whether the secondary user is present in the operating channelof the communication system.
 26. The method of claim 25, furthercomprising reducing a length of a RACH preamble.
 27. The method of claim26, further comprising sending the reduced-length RACH preamble multipletimes before an end of a RACH resource.
 28. The method of claim 26,further comprising sending the reduced-length RACH preamble once at arandom time during a RACH resource.
 29. The method of claim 25, furthercomprising: receiving, at a WTRU in a pixel-based environment, anindication of a first maximum transmit power defined for a group ofpixels of the pixel-based environment; sending a RACH preamble with thefirst maximum transmit power; receiving, at the WTRU in the pixel-basedenvironment, an indication of a second maximum transmit power specificto a location of the WTRU in the pixel-based environment; and completingthe selected RACH procedure using the second maximum transmit power. 30.A wireless transmit/receive unit (WTRU) comprising: a processorconfigured to: determine whether a secondary user is present in anoperating channel of a communication system; and perform a random accesschannel (RACH) procedure based on the determination, wherein based on adetermination that the secondary user is absent in the operatingchannel, a first RACH procedure is performed, and based on adetermination that the secondary user is present in the operatingchannel, a second RACH procedure different from the first RACH procedureis performed.
 31. The WTRU of claim 30, wherein the second RACHprocedure is based on a type of the secondary user.
 32. The WTRU ofclaim 30, wherein the second RACH procedure is configured by an eNB. 33.The WTRU of claim 30, wherein the processor is configured to receiveinformation relating to whether the secondary user is present in theoperating channel, and wherein the processor is configured to determinewhether the secondary user is present in the operating channel based onthe received information.
 34. The WTRU of claim 33, wherein theinformation relating to whether the secondary user is present or absentin the operating channel is received from an eNB, and the eNB usesfeature detection to determine whether the secondary user is present inthe operating channel.
 35. The WTRU of claim 33, wherein the informationrelating to whether the secondary user is present in the operatingchannel is received via an RRC configuration message.
 36. The WTRU ofclaim 30, wherein the WTRU sends a preamble at a power level higher thana default power level when the secondary user is present in theoperating channel.
 37. A wireless transmit/receive unit (WTRU)comprising: a processor configured to determine whether a communicationchannel is available during a random access channel (RACH) resourcebased on sensing on the communication channel; and determine a timingfor sending a RACH preamble based on whether the communication channelis available during the RACH resource, wherein the RACH preamble isdetermined to be sent during the RACH resource when the communicationchannel is available during the RACH resource, and the RACH preamble isdetermined to be sent during a subsequent RACH resource when thecommunication channel is unavailable during the RACH resource.
 38. TheWTRU of claim 37, wherein the processor is configured to send the RACHpreamble during an immediately subsequent RACH resource withoutincreasing a power of the RACH preamble when the communication channelis unavailable during a RACH resource.
 39. The WTRU of claim 37, whereinthe processor is configured to resend the RACH preamble with anincreased power during an immediately subsequent RACH resource when thecommunication channel is unavailable during a RACH resource.
 40. TheWTRU of claim 37, wherein the processor is configured to send the RACHpreamble over multiple consecutive RACH resources when the multipleconsecutive RACH resources are available.
 41. The WTRU of claim 37,wherein the processor is configured to send the RACH preamble with anincreased power during a subsequent RACH resource of multipleconsecutive RACH resources if the multiple consecutive RACH resourcesare available and the communication channel is unavailable during anentire RACH resource.
 42. The WTRU of claim 37, wherein the WTRU isconfigured to: send the RACH preamble with a default power level whenthe communication channel is available; and send the RACH preamble withan increased power relative to the default power level when thecommunication channel is unavailable.
 43. The WTRU of claim 37, whereinthe WTRU senses the communication channel by performing at least one ofan energy detection and a feature detection.
 44. The WTRU of claim 43,wherein the processor is configured to perform a feature detection fordetermining whether the communication channel is occupied by a WiFisystem and to send the RACH preamble when the communication channel isnot occupied by the WiFi system.
 45. The WTRU of claim 37, wherein theprocessor is configured to reduce a length of the RACH preamble.
 46. TheWTRU of claim 45, wherein the processor is configured to send thereduced-length RACH preamble once following a Listen Before Talk (LBT)time of the WTRU.
 47. The WTRU of claim 45, wherein the processor isconfigured to send the reduced-length RACH preamble multiple timesbefore an end of the RACH resource.
 48. The WTRU of claim 45, whereinthe processor is configured to send the reduced-length RACH preambleonce at a random time during the RACH resource.
 49. The WTRU of claim48, wherein the processor is configured to: select a random time forperforming a Listen Before Talk (LBT) procedure; perform the LBTprocedure for the selected time; and send the RACH preamble based onwhether the communication channel is available, wherein, the processoris configured to send the RACH preamble when the communication channelis available for the entire time of the LBT procedure, and to repeatperforming the LBT procedure when the communication channel isunavailable during the LBT procedure.
 50. A wireless transmit/receiveunit (WTRU) comprising: a processor configured to: select a randomaccess channel (RACH) procedure as a function of a presence or anabsence of a secondary user in an operating channel of a communicationsystem; and perform the selected random access channel (RACH) procedure.51. The WTRU of claim 50, wherein the RACH procedure is configured toreduce secondary interference.
 52. The WTRU of claim 51, wherein theprocessor is configured to perform the selected RACH procedure at leastin part by sending at least one of a RACH preamble or formatinformation.
 53. The WTRU of claim 52, wherein the processor isconfigured to perform the selected RACH procedure at least in part bydetermining a transmission power for at least one of the RACH preambleor the format information.
 54. A wireless transmit/receive unit (WTRU)comprising: a processor configured to: receive information indicatingwhether a secondary user is present in an operating channel of thecommunication system; and configure the RACH procedure when thesecondary user is present in the operating channel of the communicationsystem.
 55. The WTRU of claim 54, wherein the processor is configured toreduce a length of a RACH preamble.
 56. The WTRU of claim 55, whereinthe processor is configured to send the reduced-length RACH preamble aplurality of times before an end of a RACH resource.
 57. The WTRU ofclaim 55, wherein the processor is configured to send the reduced-lengthRACH preamble once at a random time during a RACH resource.
 58. The WTRUof claim 55, wherein the WTRU is in a pixel-based environment, and theprocessor is further configured to: receive an indication of a firstmaximum transmit power defined for a group of pixels of the pixel-basedenvironment; send the RACH preamble with the first maximum transmitpower; receive an indication of a second maximum transmit power specificto a location of the WTRU in the pixel-based environment; and completethe selected RACH procedure using the second maximum transmit power.